In Long Term Evolution (LTE), a hybrid automatic repeat request (HARQ) mechanism is used. Downlink transmission is used as an example. After a user equipment (UE) receives information carried on a physical downlink shared channel (PDSCH) in a downlink subframe, if the information is correctly received, the UE feeds back an acknowledgement (ACK) on a physical uplink control channel (PUCCH) in a corresponding uplink subframe; or if the information is not correctly received, the UE feeds back a negative acknowledgement (NACK) on a PUCCH in a corresponding uplink subframe. If no Physical Uplink Shared Channel (PUSCH) transmission is performed, the ACK/NACK is sent on the PUCCH. Once PUSCH transmission is performed, the ACK/NACK needs to be sent on a PUSCH, and the PUSCH is scheduled by using a PDCCH that is sent by a network.
LTE further supports a carrier aggregation (CA) technology, that is, a base station configures a plurality of carriers for one UE to improve a data rate of the UE.
In existing CA, the UE usually generates, according to a preconfigured carrier set and/or a preconfigured subframe set, an ACK/NACK corresponding to a downlink subframe on each corresponding carrier. For example, one UE aggregates five carriers, and downlink subframes that are preconfigured for the UE are downlink subframes that are corresponding to a current time division duplex (TDD) uplink-downlink configuration of a corresponding carrier in the five carriers. For example, if 20 downlink subframes are preconfigured for the UE, the UE needs to feedback 20 ACKs/NACKs.
With further evolution of LTE technologies, more carriers may be configured for the UE in the future. In one feedback manner, the UE needs to support feedback of an ACK/NACK with a larger quantity of bits, for example, far greater than 22 bits. This is a maximum quantity of ACK/NACK bits supported in current CA of five carriers. However, though the base station configures many carriers for the UE, a quantity of downlink subframes that are actually scheduled by the base station may be far less than a quantity of downlink subframes included in the carriers configured for the UE. For example, the base station may configure 32 carriers for the UE, and the base station can schedule, for example, 128 downlink subframes according to a TDD uplink-downlink configuration of each carrier. However, the base station may actually schedule only 20 downlink subframes. In one manner, the UE still needs to feed back ACKs/NACKs corresponding to the 128 downlink subframes to the base station, resulting in relatively high system overheads.